1. Field of the Invention
This invention relates to vehicle detection systems and, more particularly, to passive detection systems for a levitated vehicle or a levitated vehicle system, such as, for example, a MAGLEV system.
2. Background Information
Magnetic Levitated Vehicle (MAGLEV) systems are well known in the art. Examples are disclosed in U.S. Pat. Nos. 5,517,924; 5,586,504; and 6,044,770.
Most high-speed MAGLEVs are projected to run at speeds of about 150 to about 300 mph, while low-speed MAGLEVs are projected to run at speeds of up to about 30 to about 50 mph.
FIG. 1 shows a MAGLEV system 2 including a MAGLEV 4 and a guideway 6. The MAGLEV 4 moves over a suitable track having two rails 8,10. The number of rails may be modified, if desired. Extending from the MAGLEV 4 are magnetic sources (not shown), which are configured to flank each of the rails 8,10. These rails house composite coils (not shown). As the MAGLEV 4 travels along the track, its magnetic sources extend downward, with each source flanking one of the rails 8,10 and flanking the coils housed within it.
The track-based composite coils are incapable of levitating and stabilizing the MAGLEV 4 at low speeds. One alternative for addressing this low-speed problem is to affix wheels 12 to the bottom of the MAGLEV 4, in order to support the MAGLEV at certain speeds. The wheels 12 can be retracted as with conventional aircraft. Alternatively, the surface of the guideway 6 can be sloped away from the rail composite coil structure (not shown). Another alternative employs an additional coil (not shown) situated in the track.
FIG. 2 shows a conventional railroad track circuit 20 including a battery 22, a resistor 23, a track 24, and a relay 26. The feed or battery end and the relay end of the track circuit 20 are electrically connected to the two rails 27,28 of the track 24. Under conditions when a vehicle, such as a train (not shown), is not within the track circuit 20, the battery 22 energizes the coil 29 of the relay 26 through the series combination of the resistor 23, the first rail 27, the coil 29 and the second rail 28. In turn, the normally open contact 30 of the energized relay 26 closes as shown in FIG. 2.
As shown in FIG. 3, the track circuit 20 employs the shunting properties of a train""s wheels and axle (i.e., a train shunt 32) to sufficiently reduce the current in the relay coil 29 and, thus, open the normally open contact 30, in order to indicate the presence of the train (not shown) in the track circuit 20. Hence, physical and electrical contact is required between the track rails 27,28 and the train shunt 32.
U.S. Pat. No. 4,661,799 discloses an inductive detector loop for detecting the presence of a vehicle. The front end of a receiver circuit includes a parallel tuned circuit having a tuning capacitor. A method of operating the detector loop includes the steps of energizing the loop with a first signal at a first frequency, monitoring the first signal to detect the presence of a vehicle within the electromagnetic area of the loop, transmitting a signal to the vehicle to activate a transmitter in order to transmit a second signal at a second frequency which is different from the first frequency, and monitoring the loop to detect the second signal.
U.S. Pat. No. 6,100,820 discloses a vehicle detector device having at least one inductive loop used as a sensor, and a phase/amplitude controller. The prior art section of U.S. Pat. No. 6,100,820 indicates that vehicle detectors are employed for purposes of detecting vehicles in traffic, and may be used to detect the presence, type and/or speed of such vehicles. Inductive loops are permanently embedded in the roadway of a traffic route-in a lane-related manner, if necessary. Vehicle detectors of this type using inductive loops as sensors exploit the effect that loop inductance varies depending on the metallic mass of a vehicle moving in the range of the inductive loop. In order to evaluate this effect, the inductive loop is accompanied by a modified capacitor to produce a resonant circuit, which is made to resonate by an excitation circuit. The resting frequency is defined as the frequency of this resonant circuit, which arises when a vehicle is not in the detection range of the inductive loop. The resonant frequency changes from the resting frequency when the loop inductance changes, caused by a vehicle. The amount of change is proportional to the mass of the detected vehicle.
There remains a substantial need for improvement in vehicle detection systems and, in particular, to such systems for a levitated vehicle or a levitated vehicle system, such as, for example, a MAGLEV system.
This need and others are met by the present invention, which employs an inductor core in combination with a detection loop of a track circuit. The inductor core includes openings adapted to receive a length of a track circuit cable, while avoiding the ends of that cable. The inductor core is adapted to change a sensed signal of a track circuit receiver, in order to detect the presence of a levitated vehicle at the detection loop.
As one aspect of the invention, a passive detection system for a levitated vehicle comprises: at least one track circuit including a detection loop having a cable with a first end, a length and a second end, the track circuit also including a transmitter electrically connected to the first end of the cable and adapted to source a signal to the detection loop, and a receiver electrically connected to the second end of the cable and adapted to sense the signal from the detection loop; an inductor core including two openings adapted to receive the length of the cable and two openings adapted to avoid the first and second ends of the cable, the inductor core adapted to change the sensed signal of the receiver of the track circuit in order to detect a presence of the levitated vehicle at the detection loop; and a member adapted to support the inductor core from the levitated vehicle.
Preferably, the cable of the detection loop of the track circuit has a plurality of turns, and one of the openings of the inductor core is adapted to receive the turns of the cable therein. The transmitter sources a current having a first value to the detection loop before the inductor core enters the detection loop. When the inductor core enters the detection loop the transmitter sources the current having a second value. The second value is less than the first value, a count of the turns of the cable is N, and a ratio of the first value to the second value is related to N2.
As another aspect of the invention, a passive detection system for a levitated vehicle system comprises: a plurality of track circuits, each of the track circuits including a detection loop having a cable with a first end, a length and a second end, each of the track circuits also including a transmitter electrically connected to the first end of the cable and adapted to source a signal to the detection loop, and a receiver electrically connected to the second end of the cable and adapted to sense the signal from the detection loop; a plurality of members adapted to support the track circuits with respect to a guideway of the levitated vehicle system; an inductor core including two openings adapted to receive the length of the cable of one of the track circuits and two openings adapted to avoid the first and second ends of the cable, the inductor core adapted to change the sensed signal of the receiver of the one of the track circuits in order to detect a presence of the levitated vehicle at a corresponding one of the detection loops; and a member adapted to support the inductor core from a levitated vehicle of the levitated vehicle system.
Preferably, the cable of the detection loop of at least one of the track circuits includes first and second parallel conductors, first and second end segments adapted to electrically connect to the transmitter of the detection loop, and third and fourth end segments adapted to electrically connect to the receiver of the detection loop, with the first, second, third and fourth end segments being normal to the first and second parallel conductors. The inductor core may include first and second opposing E-shaped members, with each of the opposing E-shaped members having a base and first, second and third parallel legs disposed from the base, with the second parallel leg being disposed between the first and third parallel legs, with the first and second parallel legs of the first and second opposing E-shaped members forming a first opening adapted to receive the first parallel conductor, with the second and third parallel legs of the first and second opposing E-shaped members forming a second opening adapted to receive the second parallel conductor, with the first parallel legs of the first and second opposing E-shaped members being separated to form a third opening adapted to avoid the first and third end segments, and with the third parallel legs of the first and second opposing E-shaped members being separated to form a fourth opening adapted to avoid the second and fourth end segments.
The levitated vehicle may include a protection system, and the inductor core may further include a core member and an antenna element adapted to electrically connect to the protection system. The antenna element may include a plurality of windings around the core member and an electrical connection from the windings to the protection system.
Preferably, the cable of the detection loop of each of the track circuits includes first and second parallel conductors, first and second end segments adapted to electrically connect to the transmitter of the detection loop, and third and fourth end segments adapted to electrically connect to the receiver of the detection loop. The inductor core may include a first opening adapted to receive the first parallel conductor, a second opening adapted to receive the second parallel conductor, a third opening adapted to avoid the first and third end segments, and a fourth opening adapted to avoid the second and fourth end segments, in order to permit the inductor core to traverse from one of the track circuits to an adjacent one of the track circuits.